Winter Forecast/Pattern Update and Checkpoint
For reference, please access our 2018-2019 Winter Forecast issued in November right here.
Good morning y'all. Happy Monday, and I hope you all have enjoyed a wonderful weekend. This time of year always seems to pass us by so quickly; the holidays certainly add to the speed of which time seems to pass. Before we know it, it will be January and we will be buried in s....actually, let me digress for a moment. If you really take a moment to think about it, it feels like this "Winter" has been going on for months already. You can thank the early/mid November snowfall for that. Since then, we've been on a roller coaster of high and low emotions, with a few head-fakes in regards to the long range pattern. Medium and long range ensemble guidance has not helped in that regard, as they have been too quick to pull the trigger on -EPO/-NAO blocking a few times already in December. The larger scale hemispheric pattern simply hasn't aligned exactly as we have needed it to, and there have been a few misaligned pieces (MJO in particular).
The current upcoming late December period looked quite favorable for a while, but most long range ensemble guidance did a very poor job of resolving the effects of EAMT as well as the MJO. The current MJO amplitude exceeded most ensemble forecast guidance at a 8-14 day lead time. The North Pacific Jet retraction did occur, but we are also seeing a large-scale retrograde of the North Pacific pattern. Without much impetus to prevent this, the Aleutian low will only be present for a day or so before it retrogrades back towards a more unfavorable position and a more notable North-Pacific ridge anomaly develops. This will limit the favorable pattern in the Eastern US quite a bit, and while a gradient pattern may eventually develop, it likely will be largely modulated by a Southeast Ridge that will meet little resistance. The wild card will be the NAO domain, which a negative modality may favor New England late this month for a few events. See the below image -- no bueno. I expect our initial call of a warmer/less snowy than normal December in the Northeast will be correct.
For the most of us, however, this will require more patience and I don't see the late month period to be as favorable as some others at this juncture. The hemisphere is going to reset itself once again. However, I think this requires some larger-scale perspective. Back in early November in our 2018-2019 Winter Forecast we specifically discussed this evolution, with the potential for a briefly favorable period near the holidays. However, it was also discussed ad-nausem that the time frame to watch most carefully was the early to middle part of January. That has not changed, and in fact confidence has probably doubled that this time frame will be extremely favorable.
Most long range model guidance is in agreement on the overall progression of the wave guide. The MJO will continue its progression, coming around the bend and largely expected to weaken. However, the current (Arguable ) - MT state is expected to flip, with the GEFS and ECMWF both in good agreement that the next +MT pulse will begin later this month. EAMT is expected in + territory as we move into the early part of January. Most importantly, for the first time this winter, this will align well with tropical forcing and also aid in the development of a more favorable North Pacific jet.
When you take the sum of these parts and add in the developments in the stratosphere, the true potential breadth and depth fo the situation becomes more apparent. Almost all ensemble guidance is now in good agreement that another notable W1 event will displace and/or split the stratospheric polar vortex, with a complete reversal of zonal winds at 10hPa and the potential for further depth. A subsequent W2 event is not out of the question. In other words, the stratospheric polar vortex is expected to remain extremely weak, perhaps on the periphery of climatology, and the potential exists for a SSW in late December or very early January. While the exact evolution is indeterminate, the percentage chance of a SSW is much higher than normal, and the weakened state of the stratospheric polar vortex significantly enhances the chances for very anomalous high latitude blocking.
I expect the state of the North Pacific to improve dramatically as we move into early and Mid January, and I expect the stratospheric evolution to additionally aid in the development of high latitude blocking. With tropical forcing in a more favorable state, the development of an Aleutian low appears probable. The stratospheric vortex will remain very weakened and supportive of high latitude blocking (-NAM?) - and as a result, I expect a very favorable pattern for colder than normal air and significant winter storms will evolve across the Northeast states by the middle of January, perhaps as early as January 7th and continuing through January 25th. (those dates will need to be amended and honed in)
It is obviously far too early to discuss any specifics, storm threats, intangibles, etc. However, I felt it necessary to touch base on this time period - which currently looks likely to feature the alignment of many features across the hemisphere that we so often struggle to get to work in our favor. My suggestion is to relax and enjoy any snow threats that come prior to that. We are a few weeks away still from this favorable period, but it will be worth the wait and then some.

Several months delayed here, I realize; between life, other endeavors, etc., I have finally progressed through the entirety of this thread. I must say - you all have quite effectively conveyed this information. Very nice work.

SNIPPED.

Welcome to the Teleconnections thread Tom (@Isotherm). I know that Geoff (@33andrain), Pat (@NJwxguy78) and Zac (@Snowy Hibbo) and the regular posters on here have been keen to persuade you and some other professional meteorologists to contribute on this thread. I started exchanging PMs with Zac on a UK forum where I started a Teleconnections thread in January. One of my goals had been to create an online library for all the specialist papers embracing teleconnections. The UK forum was slow to deal with this and it never got off the ground. Then Zac told me that he was launching a specialist thread on this forum and asked a few of us for our assistance. Geoff and Pat were so accommodating and willing to support my library idea that this convinced me to make this forum my main focus. Zac and especially Malcolm (@Blessed Weather) helped a lot with the development and we launched the Teleconnections Research Portal 3 months ago. This is to support this thread and where relevant, other specialist threads on this forum.

You raise some interesting points. It's surprising how few professionals and met offices properly embrace AAM and the torques. The whole process is a very important part of understanding the background signals and upcoming changes. Quite a few long range forecasts refer to the ENSO state, the MJO and SSTs but usually miss out on AAM and the torques. I believe that we have almost gone as far as we can in "rapidly" improving the reliability of short to medium range forecasts (up to 10 to 15 days out) with super computers, satellite observations and nwp developments and further progress will be more limited. On the other hand, trying to make sense of chaos theory is a challenge but this is necessary to improve long term and seasonal forecasts. By accepting that these forecasts need to be at a more general level relating to broader pattern changes and not a precise "in my back yard" prediction for a given date or time, we can make huge progress. This is embracing all the teleconnections and endeavouring to understand how they interact and which ones dominate at particular times. With climate change the goal posts are constantly moving. The global warming debate has become highly political and is dominated by who controls the purse strings with claims and counter claims at each end of the argument which are often exaggerated and conspiracy theories abound. If only almost all scientists could be allowed to focus on a balanced approach to get at the true facts.

Turning to your excellent idea about a "YouTube" presentation - teleconnections is such a vast subject and the more I learn about it, the more I realise how much more there is to learn. I consider my own understanding of the GWO/AAM/FT/MT/MJO/QBO/ENSO is at a pretty basic level. Searching for, reading and reviewing papers and video presentations in recent years has helped add to my knowledge formed over 58 years of being a keen amateur weather enthusiast (since aged 7) but I am certainly not at a level to produce a video presentation. The problem is that we have some of the professionals who have the skills and specialist knowledge to do this but they have limited time as well as financial constraints. Other professionals and specialist researchers generally prefer to exchange views and presentations at an advanced and very technical level. It is this advanced knowledge that is required to produce even the simpler presentations. Perhaps a retired professional who retains their enthusiasm might be persuaded to do this. I and a small group of us have been in touch with Ed Berry (who worked with Dr Klaus Weickmann, now retired) who I posted about on page 3 of this thread, is still working. We have also been in touch with Victor Gensini. Both Ed and Victor specialise in GWO/AAM etc. They are looking for financial support and Victor has applied for an NSF CAREER award. If he (or they) can obtain this backing, then they may have time to produce one or a series of videos. To get more people "hooked" on this subject we need to give it as much publicity as possible. One of today's keen students may become a specialist in due course.

One of the points of the Research Portal is to put papers into categories by subject and topic. I have another idea which is to develop a "Learning Area" within the portal. We have been adding a whole range of papers and video presentations from highly technical thru to learning about the basics. I could copy the ones on the basics and definitions etc into the Learning Area. I already intend to continue to provide links to the many simple presentations out there, including many from YouTube. As you say, the problem is that there are very few which cover AAM etc even indirectly. I suggest that if we cannot persuade any one person to produce a comprehensive AAM guide, that a number of us could put together different components or pieces of the jig-saw. I (and others) will continue to add relevant papers and videos to the portal. I may launch the Learners Area this winter which will make it easier to review these contributions - some of which can be done on this thread and then we can see where the gaps are and we can endeavour to address these. Once we feel that we have assembled sufficient input we might be in a position to put a presentation together We already have an "Interactive Area" in the portal which could be used for co-ordinating ideas and exchanging views. Zac, Malcolm and I also have a PM thread on here for monitoring this thread and the portal. We would be happy to include you in this discussion.

Finally, I have deliberately, set this all out on here, so that any other forum members who have any ideas, feedback or contributions to make on his subject can get involved too. David

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Welcome to the Teleconnections thread Tom (@Isotherm). I know that Geoff (@33andrain), Pat (@NJwxguy78) and Zac (@Snowy Hibbo) and the regular posters on here have been keen to persuade you and some other professional meteorologists to contribute on this thread. I started exchanging PMs with Zac on a UK forum where I started a Teleconnections thread in January. One of my goals had been to create an online library for all the specialist papers embracing teleconnections. The UK forum was slow to deal with this and it never got off the ground. Then Zac told me that he was launching a specialist thread on this forum and asked a few of us for our assistance. Geoff and Pat were so accommodating and willing to support my library idea that this convinced me to make this forum my main focus. Zac and especially Malcolm (@Blessed Weather) helped a lot with the development and we launched the Teleconnections Research Portal 3 months ago. This is to support this thread and where relevant, other specialist threads on this forum.

You raise some interesting points. It's surprising how few professionals and met offices properly embrace AAM and the torques. The whole process is a very important part of understanding the background signals and upcoming changes. Quite a few long range forecasts refer to the ENSO state, the MJO and SSTs but usually miss out on AAM and the torques. I believe that we have almost gone as far as we can in "rapidly" improving the reliability of short to medium range forecasts (up to 10 to 15 days out) with super computers, satellite observations and nwp developments and further progress will be more limited. On the other hand, trying to make sense of chaos theory is a challenge but this is necessary to improve long term and seasonal forecasts. By accepting that these forecasts need to be at a more general level relating to broader pattern changes and not a precise "in my back yard" prediction for a given date or time, we can make huge progress. This is embracing all the teleconnections and endeavouring to understand how they interact and which ones dominate at particular times. With climate change the goal posts are constantly moving. The global warming debate has become highly political and is dominated by who controls the purse strings with claims and counter claims at each end of the argument which are often exaggerated and conspiracy theories abound. If only almost all scientists could be allowed to focus on a balanced approach to get at the true facts.

Turning to your excellent idea about a "YouTube" presentation - teleconnections is such a vast subject and the more I learn about it, the more I realise how much more there is to learn. I consider my own understanding of the GWO/AAM/FT/MT/MJO/QBO/ENSO is at a pretty basic level. Searching for, reading and reviewing papers and video presentations in recent years has helped add to my knowledge formed over 58 years of being a keen amateur weather enthusiast (since aged 7) but I am certainly not at a level to produce a video presentation. The problem is that we have some of the professionals who have the skills and specialist knowledge to do this but they have limited time as well as financial constraints. Other professionals and specialist researchers generally prefer to exchange views and presentations at an advanced and very technical level. It is this advanced knowledge that is required to produce even the simpler presentations. Perhaps a retired professional who retains their enthusiasm might be persuaded to do this. I and a small group of us have been in touch with Ed Berry (who worked with Dr Klaus Weickmann, now retired) who I posted about on page 3 of this thread, is still working. We have also been in touch with Victor Gensini. Both Ed and Victor specialise in GWO/AAM etc. They are looking for financial support and Victor has applied for an NSF CAREER award. If he (or they) can obtain this backing, then they may have time to produce one or a series of videos. To get more people "hooked" on this subject we need to give it as much publicity as possible. One of today's keen students may become a specialist in due course.

One of the points of the Research Portal is to put papers into categories by subject and topic. I have another idea which is to develop a "Learning Area" within the portal. We have been adding a whole range of papers and video presentations from highly technical thru to learning about the basics. I could copy the ones on the basics and definitions etc into the Learning Area. I already intend to continue to provide links to the many simple presentations out there, including many from YouTube. As you say, the problem is that there are very few which cover AAM etc even indirectly. I suggest that if we cannot persuade any one person to produce a comprehensive AAM guide, that a number of us could put together different components or pieces of the jig-saw. I (and others) will continue to add relevant papers and videos to the portal. I may launch the Learners Area this winter which will make it easier to review these contributions - some of which can be done on this thread and then we can see where the gaps are and we can endeavour to address these. Once we feel that we have assembled sufficient input we might be in a position to put a presentation together We already have an "Interactive Area" in the portal which could be used for co-ordinating ideas and exchanging views. Zac, Malcolm and I also have a PM thread on here for monitoring this thread and the portal. We would be happy to include you in this discussion.

Finally, I have deliberately, set this all out on here, so that any other forum members who have any ideas, feedback or contributions to make on his subject can get involved too. David

Well said, David.

And I completely concur; the paucity of available videos is multifactorial, including time constraints and the fact that advanced knowledge is a prerequisite for teaching more rudimentary concepts (e.g., in order to teach high school science, a master's in a science is typically necessary). I think most forecasters are selling themselves short by refusing to delve more deeply in such topics as AAM, GWO, and torques. Since I have learned about these teleconnections and their concomitant functions more extensively, I could not have envisioned forecasting long range without them, honestly. It's much more limiting to forecast w/o them.

Thanks for the PM invite, too. I'd be happy to join (just as a disclaimer, my time will become even more limited going forward).

It is unfortunate that there aren't more videos on youtube re: these topics. I saw the research portal, and you and your colleagues have done a very good job setting that up.

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Prof. Jason Furtado has just written a very interesting 'guest article' for the NOAA/Climate.gov website giving details of his research into the role that the South Pacific Oscillation (SPO) plays in helping determine the type and strength of developing EL Ninos. The article includes many informative charts.

Key extracts:

......let’s consider the evolution and development of an El Niño event. In June when an El Niño event is developing, warm water anomalies are already present in the central tropical Pacific. For development to continue, those warm central tropical Pacific SSTs have to build eastward and amplify during Northern Hemisphere summer and early fall. This eastward propagation of anomalies is driven by westerly winds and the formation of Kelvin Waves in the ocean in the eastern tropical Pacific, thus allowing waters to get warmer there. Since the SPO modulates the strength of the South Pacific trade winds in the eastern tropical Pacific, and it is most active during JJA, the phase and magnitude of the SPO can either help or hurt those Kelvin waves and the winds during the critical growth phase for ENSO.

If the SPO is in the positive phase (i.e., a weaker South Pacific subtropical high), then the southeasterly trade winds weaken, which reduces the cold-water upwelling in the eastern tropical Pacific and allows for easier eastward propagation of the warm waters from the central tropical Pacific to the eastern tropical Pacific.

However, if the SPO is in the negative phase (i.e., a stronger South Pacific subtropical high), then the southeasterly trade winds intensify, and the cold-water upwelling in the eastern tropical Pacific also increases. These two factors create an environment hostile for eastward expansion of the warm waters. Thus, the warm SST anomalies tend to remain in the central tropical Pacific.

.......we identified all El Niño events (regardless of flavor) from 1950-present and then examined what the magnitude and sign of the JJA SPO was for that year. Using only that information, we predicted what the flavor of that El Niño event would be the following winter. The results indicate that our simple prediction scheme correctly predicted the flavor of the event nearly 3 out of 4 times.

What does the SPO have to say about the expected flavor of this year’s El Niño event? The figure above illustrates that the SST warming thus far over the eastern tropical Pacific is spotty with evidence of subsurface warming present. Note that south of the Equator, however, there is an expanse of quite cold waters. More importantly, the SLP pattern in the South Pacific resembles a negative SPO signature. Indeed, for June 2018, the SPO index was about -1.3, and the SLP anomaly pattern in the South Pacific thus far for July also suggests a negative SPO value for the month. Without a substantial turnaround for the SPO in August, the JJA SPO for 2018 could turn out negative. Thus, based on what I argued above, if an El Niño event forms this upcoming winter, it will most likely be a weak/CP El Niño event. Luckily, I am not totally alone in this prediction. The latest forecast from the NMME models (below) hints at a weaker/CP El Niño event evolving this winter.

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And I completely concur; the paucity of available videos is multifactorial, including time constraints and the fact that advanced knowledge is a prerequisite for teaching more rudimentary concepts (e.g., in order to teach high school science, a master's in a science is typically necessary). I think most forecasters are selling themselves short by refusing to delve more deeply in such topics as AAM, GWO, and torques. Since I have learned about these teleconnections and their concomitant functions more extensively, I could not have envisioned forecasting long range without them, honestly. It's much more limiting to forecast w/o them.

Thanks for the PM invite, too. I'd be happy to join (just as a disclaimer, my time will become even more limited going forward).

It is unfortunate that there aren't more videos on youtube re: these topics. I saw the research portal, and you and your colleagues have done a very good job setting that up.

I agree with this very much. The hardest obstacle remains one of parochial attitudes towards the GSDM and pre-conceived attitudes towards even reading up on the literature that has been so helpfully provided here and elsewhere and which is such valuable additional insight into the global wind-flow budgets that add an extra dimension to medium-long range forecasting and NWP analysis.

The next hardest task is breaking down the components into layperson English so that any audience is prepared to keep an open mind and read analysis provided and not give up because of its apparent complexities. Hence they become subscribed themselves to its use. Not on some elite cult club basis, but simply as a means to advance their own and others understanding of the complexities of the global atmosphere.

For all the posts I have made mostly elsewhere that utilise the GSDM extensively within my own style of weather pattern enthusiasm study over an increasing period of time, these challenges still remain omnipresent and can be a source of negative feedback on occasion and subsequent frustration! Some of these cynical and rather condescending minds are indeed intellectual enthusiasts who deem the concept model to be a poor relation to peer reviewed literature . When in fact a higher profile would enhance its ground breaking potential in the same way as for example stratospheric analysis finally became mainstream in the last decade beyond the paywall literature and parochial attitudes towards it that had existed right up to about 2008/2009.

Hopefully eventually the GSDM will also achieve the same wider use and acceptance.

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After its annual summer break the Polar Vortex is set to return thanks to increasingly weak insolation (warming from the sun) at higher latitudes allowing the upper stratosphere to cool. The GEFS forecast suggests this will happen around August 24th with the return of weak westerly Zonal Mean Zonal Winds at 10hPa 60N. During the Fall I'll do a comprehensive post on the various teleconnections that are likely to impact the PV and thus influence our weather over the winter months - including MJO, QBO, ENSO, SST and more - and I'll include reference to the many excellent papers held in the 33andrain Research Portal.

In the meantime, welcome back PV - we look forward to you having a very disturbed winter!

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QBO & ENSO on the change – the implications for the Polar Vortex and chances of SSW this coming winter

As we enter fall and head towards winter it’s my intention to post regularly on this thread on developments in the stratosphere and in particular the chances of a Sudden Stratospheric Warming (SSW).

I’ll start by looking at two important teleconnections - the QBO and ENSO – which are currently in transition from one phase to another. The QBO has been in the easterly phase but is now moving towards a westerly phase.

This quote from the World Climate Service:

“The 30mb QBO index is rising fast now - a positive QBO phase may well emerge by winter. If so, and taken in isolation, this would be a positive AO/NAO signal for winter.”

Another way of looking at how the QBO is changing is to compare the following marked-up ECM charts which show last winter’s easterly QBO at 30hPa above the equator (circled) and strengthening Polar Vortex (westerly winds approx 25 m/s) at 10hPa 60N (starred) compared with the forecast for 6th Sept 2018 showing the developing westerly QBO with winds descending through the stratosphere and a fledgling PV with gentle westerly winds at under 5 m/s.

So what are the implications for the Polar Vortex and the occurrence of a Sudden Stratosphere Warming (SSW) this coming winter? According to the research paper Changes in Frequency of Major Stratospheric Sudden Warmings with El Niño/Southern Oscillation and Quasi-Biennial Oscillation

"When the QBO is westerly, the probability (of a major SSW) increases for El Nino and decreases for La Nina, compared to Neutral."

This table from the research looks at the 56 years of the NINO3.4 SST Index and finds that only 9 winters have experienced an El Nino at the same time as a wQBO. But of these 9 winters, 6 experienced a SSW (66.7% of such winters).

But of note, in the research paper Northern Hemisphere Stratospheric Pathway of Different El Niño Flavors in Stratosphere-Resolving CMIP5 Models involving the Coupled Model Intercomparison Project, models show a significantly warmer and weaker polar vortex during East Pacific (EP) based El Niño (EN), but no significant polar stratospheric response is found during Central Pacific (CP) EN. The model simulations of 48 EP events, resulted in 32 (66%) occurrences of a SSW. Whilst in 43 simulated CP events, 20 (46%) resulted in a SSW.

"This is a result of differences in the timing of the intensification of the climatological wavenumber 1 through constructive interference, which occurs earlier in EP than CP events, related to the anomalous enhancement and earlier development of the Pacific–North American pattern in EP events. The northward extension of the Aleutian low and the stronger and eastward location of the high over eastern Canada during EP events are key in explaining the differences in upward wave propagation between the two types of El Niño."

I’ll revisit this post to track ongoing changes in ENSO and QBO status - as the above assumes a continuation towards change of phase - and will also take a look at other teleconnections likely to impact the Polar Vortex – such as MJO and solar activity – as we move further into the Fall.

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I have been away dealing with some personal issues, but now I am back. Now it's time for me to get my head back in the game, and have a little look at how we are tracking heading into autumn (well for the NH at least).

For a bit of fun to start, here is the CFS Monthly charts (moving GIF) of the stratosphere over the Arctic.

The takeaway here is a pretty average entry into winter stratosphere wise, but perhaps a tad early and slightly more dramatic exit (SSWs in February?). Definitely something to watch, but not to dwell upon.

My pet chart, the CFS Weekly model at 10hPa 60 degrees North (note the inclusion of GEFS ensembles as well).

There is a lead with the GEFS ensembles mean that show a weaker than normal progression in the next two weeks, countering the recent slightly above average progress of the strengthening SPV. The CFS Control seems to follow on from these GEFS ensembles, but the general CFS trend shows typical growth of the SPV until mid October. Then all of the CFS ensembles in a major consensus weaken (-AO drop possible around here), and stay weak throughout November into December. This is a very unusual event, but this could prompt a -AO stratospheric setup, which would promote a similar tropospheric regime. And of course the desired effects for the Eastern United States. But I am probably reading too much into this rather unlikely and complex forecast, with various unforeseen implications.

But I am going to move on from the stratosphere. There's so much that still needs to be calculated in that area that we can't foresee at this very moment, such as Siberian snow cover, ENSO, etc.

Let's begin the next discussion with another CFS chart (really well used today clearly...). This is a follow-up or a companion, or really just some thoughts on @Tamara's post in the winter thread as mentioned above.

The CFS GWO chart from Victor Gensini displays a clear trend of +AAM progression from our current neutral position. This is because CFS's current strong Nino forecast, so it will show a tendency for that way.

Though even with this Nino bias it now has, could it be on the money?

A bit of keen spotting gets you this image (GFS TT MSLP)

You could say this looks like any old weather chart, but to any keen GWO enthusiast, it looks like a production chamber for a +EAMT. Notice the high over Kazakhstan and the low over Tibet, and then the bars in between. This carries over the mountains and into the uppers, creating a jetstream moving into China (movable GIF)

This ultimately equals a North Pacific Jet extension, although one that isn't potentially influential to the West Coast of the US.

These are the little quirks we need to look for to see where these events occur, so we can spot the downstream effects. This will ultimately help create some sort of positive GLAAM state with the support of other torques. I don't suggest it to the proportion of CFS' proposal, with no other major modelled +MT events, but maybe I am looking at the wrong areas. The FT has been slowly increased over the past few days, but it is currently stagnant with a -FT event in the Southern Ocean. Nonetheless, doesn't change my conclusion.

.

Feel free to rebut or discuss, as usual.

Just as a quick post script note to @Blessed Weather 's post about the QBO, my thoughts before my (sort of) hiatus were that we would get across the line with a -QBO winter. But increasingly including with guidance from EPS and GFS, it seems clear that we may cross the line just before or during winter. This would probably provide a fairly neutral effect from the QBO in isolation. But as he said, a key issue this autumn to watch as it progresses.

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Great post @Snowy Hibbo. I particularly like the chart with the strong jetstream which seems to be a direct hit on the Mongolian Mountains. We'll be looking for similar set-ups in winter as research shows that mountain torque in that area can have a big impact on the stratosphere. In 'ideal' conditions this can reduce the stratospheric jet strength by 1/3 and increase the chance of a SSW from 0.08/year to 0.60/year. Link to Paper.

Back to the El Nino (EN) discussions. I've just found another paper on the impact of an eastern versus central Pacific based EN.

The changing impact of El Niño on US winter temperatures

"....the impact on US winter temperatures is different for the different types of El Niño. While the conventional Eastern-Pacific El Niño affects winter temperatures primarily

over the Great Lakes, Northeast, and Southwest US, the largest impact from Central-Pacific El Niño is on temperatures in the northwestern and southeastern US."

So of interest is the latest blog from PerspectaWeatherwhich is clearly coming down on the side of a central Pacific based El Nino:

El Nino conditions are starting to appear in the Equatorial Pacific Ocean and its specific location raises the prospect of a cold and snowy winter in the Eastern US.

"The first sign of an "central-based" El Nino may be occurring right now with a noticeable area of warmer-than-normal water situated in the central Pacific. In addition, some computer forecast models (e.g., NOAA CFSv2, JAMSTEC) suggest the upcoming winter will indeed feature a "central-based" El Nino. In recent history, strong El Nino’s that were “eastern-based” generally have been associated with warmer-than-normal winters in the eastern US whereas “central-based” weak-to-moderate El Nino’s have been correlated with cold and snowy winters. For instance, two strong and "eastern-based" El Nino’s that resulted in warm winters in much of the eastern US took place during the winters of 1972-1973 and 1997-1998. On the other hand, two weak-to-moderate El Nino's that were "central-based" and resulted in cold and snowy winters occurred in 2002-2003 and 2009-2010."

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A REVIEW OF A BRILLIANT YOUTUBE PRESENTATION ON THE NAO AND CLIMATE VARIABILITY IN THE NORTH ATLANTIC

I've been busy adding yet more papers and presentations to the Research Portal and I'm currently focusing on the North Atlantic Oscillation (NAO). I found a paper entitled: "Ski﻿lful Predictions of the Winter North Atlantic Oscillation One Year Ah﻿ea﻿d" published in 2016 by a leading team at the UK Met Office.﻿﻿﻿﻿﻿ Unfortunately, the full paper is still behind a paywall but on researching the citing literature I found this superb YouTube presentation made by the same authors last year (a few months later) with a slightly modified title. In this post, I shall review this presentation which belongs equally on the Teleconnections thread as well as on the Climate Change thread, so it's going on to both!

From there you will find a direct link to the full presentation. It's nearly an hour long but is well worth the time - so pour yourself a glass of your favourite tipple and sit back and enjoy. You'll see that I also provide the link there to the "Nature GeoScience" website entry and anyone who is a subscriber can view the full paper. Here's a copy of the abstract:

"The winter North Atlantic Oscillation is the primary mode of atmospheric variability in the North Atlantic region and has a profound influence on European and North American winter climate. Until recently, seasonal variability of the North Atlantic Oscillation was thought to be largely driven by chaotic and inherently unpredictable processes. However, latest generation seasonal forecasting systems have demonstrated significant skill in predicting the North Atlantic Oscillation when initialized a month before the onset of winter. Here we extend skilful dynamical model predictions to more than a year ahead. The skill increases greatly with ensemble size due to a spuriously small signal-to-noise ratio in the model, and consequently larger ensembles are projected to further increase the skill in predicting the North Atlantic Oscillation. We identify two sources of skill for second-winter forecasts of the North Atlantic Oscillation: climate variability in the tropical Pacific region and predictable effects of solar forcing on the stratospheric polar vortex strength. We also identify model biases in Arctic sea ice that, if reduced, may further increase skill. Our results open possibilities for a range of new climate services, including for the transport, energy, water management and insurance sectors."

Now to the presentation itself. I should emphasis that all of us can take something out of this presentation as it provides some simple explanations with clear charts for early learners as well as some much more technical aspects. The main presenter, Dr Nick Dunstone, heads up the "Climate Dynamics Group" which is part of a team of over 200 research scientists based at the Hadley Center, a section of the UK Meteorological Office. Nick has been studying climate variability for many years and completed a PhD in Astrophysics in 2008. The first half of the presentation focuses on climate variability and although slightly orientated towards the UK and Europe, there is plenty on the North American climate impacts too. There is a great explanation of the "AMO" (Atlantic Multidecadal Oscillation) also known as the "AMV" (Atlantic Multidecadal Variability) and a long section on "decadal climate variability". The second half is on the "NAO" with the focus on predicting winter patterns and related climate impacts for not only one year ahead but also 2 years ahead with seasonal and interannuual timescales.

There is a look into climate prediction models. The UK Met Office "used" to use separate computer systems and models for assessing shorter term forecasts and longer term climate patterns and that is still how most international research (including that in the US) is carried out. Their new supercomputer came into use two years ago. This enables both short term and long term assessments and predictions to be conducted by extending the paramiters of the same computer models. This has produced some much more accurate results. The term "hindcasting" has been used increasingly in recent years. This is where a predictive model or individual programme's reliability (strengths and weaknesses) can be tested by inputting past data to see how accurate the results are - measured against what is known to actually happen. This includes all the short term (as well as the longer term) variables and where the new "single" system approach has enormous advantages over totally independent systems. it's also advantageous to have all this under one roof - some countries use completely separate, offices, research teams and even organisations and yet this is all so inter-related. When assessing and comparing human influenced climate change and natural climate variability this more integrated type of measurement and assessment should prove to be invaluable to get at the real facts. The UK Met Office take a balanced and open minded approach to climate change and this presentation is a great demonstration of that neutral position which is so important to avoid all the politics and hype at both extremes of the global warming and climate change debate.. Here is a small selection of slides to whet your appetite but you'll need to watch and listen to the full presentation to get the real benefit :

I hope that you can now see why this post belongs on both the Teleconnections and the Climate Change threads. David

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ENSO conditions are currently neutral but slowly progressing towards a weak El Nino (EN) with US/NOAA and the Japan Meteorology Agency (JMA) both suggesting a 60% chance of weak EN during the fall and the Australian Bureau of Meteorology (BOM) going for a 50% chance. This summary from BOM on Sept 11th:

The central and eastern tropical Pacific Ocean are warmer than average, with greatest warmth in the central to western Pacific (NINO4; +0.6 °C), while water below the surface remains somewhat warmer than average. Atmospheric indicators generally remain neutral, although trade winds are slightly weaker over parts of the western Pacific. A weakening of the trade winds is one of the most important precursors at this point for any possible El Niño, and will be watched closely.

The easterly (trade) winds are expected to be near normal or above normal from the central to eastern equatorial Pacific, and eastward migration of the subsurface warm waters from the western equatorial Pacific to the central part is expected to be disturbed in early boreal autumn. After that, the subsurface warm waters are expected to migrate eastward and increase SST anomalies in the eastern equatorial Pacific.

As a final point, it is worth bearing in mind the recent research by Prof Jason Furtado about the relationship between the South Pacific Oscillation (SPO) and EN. The development of an EN sees warmer sea surface temps (SSTs) build in the western and central Pacific and propagate east on westerly winds. (Link to paper in Research Portal)

Through August 2018 and into Sept there continues to be relatively high pressure over the South Eastern Pacific and this fits with the SPO being in a negative phase. Furtado’s research shows the SPO modulates the strength of the South Pacific trade winds in the eastern tropical Pacific and if these persist it supports the upwelling of cold-water in the eastern tropical Pacific. This stops the e﻿astward propag﻿ation o﻿f the warm SST an﻿﻿omalies and inhibits the development of the traditional (east based) EN and increases the likelihood of a Central Pacific (Modoki) based EN.

The upwelling of colder water in the eastern tropical Pacific can be seen holding back the progression east of warm SSTs in the following NOAA SST animation. (Note: unfortunately this animation will auto-update over time and eventually become irrelevant to this post).

In a recent tweet (Aug 30th) Prof. Furtado continues to favour the development of a CP EN.

Footnote: It should be noted that JMA uses a different definition of what constitutes an EN to NOAA's definition, in particular the ENSO Region. Here's their definitions and a chart showing the Regions:

NOAA - El Niño (La Niña) is a phenomenon in the equatorial Pacific Ocean characterized by a five consecutive 3-month running mean of sea surface temperature (SST) anomalies in the Niño 3.4 region that is above (below) the threshold of +0.5°C (-0.5°C).

JMA - JMA defines that the El Niño (La Niña) is such that the five-month running mean SST deviation for NINO.3 continues +0.5°C (-0.5°C) or higher (lower) for six consecutive months or longer.

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An update to my post above (Aug 31st). The 30mb Equatorial Zonal Mean Zonal Wind index has continued it's sharp upward trend and the World Climate Service is now saying a Westerly QBO by winter is in "little doubt".

Edit: My apologies to early readers - my original posting said "Easterly QBO in little doubt" and this should have said "Westerly QBO in little doubt" as the QBO index looks like crossing the line between negative (easterly) and positive (westerly during the late fall/early winter.

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An ostensible shift occurred w/ respect to the forcing paradigm from mid July-Aug to early-mid September; specifically, a more Nino-esque regime dominated through mid/late summer (which was reflected in other proxies as well such as the GWO, AAM), while, thus far in September, we've taken a step backward w/ respect to Nino progression. This is expected in generally very weak events (that is, occasionally countervailing tendencies / irregular patterns); however, certainly, if a more Nina-esque atmospheric regime attempts to persist into October, it could augur a different sensible weather outcome for the ensuing winter. My personal NAO indicator - though it's in the early stages of the monitoring period - is suggestive of a +NAO modality for the ensuing winter. However, I'll need through early November to incorporate all the data.

Hi Malcolm, thank you for a great post and I really liked the way that you used several different sources to pull together a good consensus overview of the "still" generally predicted movement towards a weak El Nino this fall. In a minute I will show some figures that indicate that there has been yet another set back in the progress towards that elusive El Nino.

In recent months we have both been posting a number of updates on the ENSO changes. Initially, we were posting these on this Teleconnections thread where they belong. Then we sometimes migrated to the Hurricane thread as there is such a strong Teleconnection between ENSO changes and the impacts on the Atlantic and east Pacific hurricane seasons. Last month there was an ENSO discussion on the Countdown to Winter 2018/19 thread and I decided to place one of my comprehensive updates on there. I see that an "El Nino 2018/19?" thread was started off briefly but has now been archived - very confusing. From now on, I shall take your lead and keep all my ENSO posts on here and perhaps give them a plug on the hurricane when it's relevant to a post on there. It'll be great if we can get an ENSO debate going on here and I see that while I'm preparing this post, Tom @Isotherm has just posted on this topic.

It's amazing how quickly regional SSTs can change so quickly and there has been a real battle going on in the Pacific Nino regions. The changes have been erratic to say the least. I haven't got much time now, so I'll post these charts and then come back to my main point.

Nino 4 rose strongly during the first half of August but fell sharply later in the month before rising again until yesterday..

Meanwhile, the key Nino 3.4 region has fallen back to its lowest level in 3 months. More below.

Nino 3 (central/east Pacific) which has been behaving quite differently to Nino 4 (central/west Pacific) has struggled to remain +ve.

Just to complete the abrupt turnaround Nino 1+2 (east Pacific) has recovered strongly!

I won't go into any reasons now but will just make a mathematical point. As you point out, we need three consecutive months where the Nino 3.4 region has an average SST anomaly of +0.5c or higher to meet the accepted definition of an El Nino episode. NOAA "were" going for a 60% chance of getting there in the fall and they clarify that as S/O/N. Well it has been averaging more like +0.15c for the first half of September. To average more than +0.5c for the whole of September it will need to have values quickly rising to +0.85c or higher to get there. With the ssts moving down not up, I'm almost certain that we can discount September from the equations.I mentioned this in an ENSO/SST post on the Hurricane thread last week. So at the very least a one month delay and pushing back the chances of an El Nino developing closer to the winter.

IMPORTANT EDIT: Malcolm @Blessed Weather has kindly reminded me that the NOAA definition is somewhat ambiguous (and I completely concur) and is a little longer and goes beyond the 3 month (or season) rolling periods (it must be averaged over 5 consecutive seasons for their table to go blue for La Nina or red for El Nino episodes) and this changes the maths to some extent! I am preparing another post right now, dealing exactly with this and also all the different definitions used by different countries

You quoted the NOAA weekly ENSO report which I also often focus on. Their weekly updates with their headline (60% chance of Nino in the fall - S/O/N and 70% during winter - D/J/F) is actually only updated once a month. Their monthly "ENSO Discussions" report, ironically, came out the day after your post - it's always published on the 2nd Thursday of each month. Her'e the link to it: http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.pdf We can expand on NOAA's views and reasons as part of our debate but I'll show this now:

Extract:

Synopsis: There is a50-55% chance of El Niño onset during the Northern Hemisphere fall 2018 (September-November),increasing to 65-70% during winter 2018-19. ENSO-neutral continued during August, as indicated by a blend of slightly above- and belowaverage sea surface temperatures (SSTs) across the equatorial Pacific Ocean (Fig. 1). Over the last month, the westernmost Niño-4 region was the warmest (latest weekly value was +0.5C), while the Niño-3 and Niño-3.4 regions were weakly positive, with Niño1+2 remaining negative (Fig. 2). Subsurface temperature anomalies (averaged across 180°-100°W) were positive (Fig. 3), with an increase in aboveaverage subsurface temperatures in the central Pacific and slight expansion of negative anomalies in the eastern Pacific (Fig. 4). Convection returned to near average over the Date Line, and was slightly enhanced over Indonesia (Fig. 5). Low-level westerly wind anomalies re-developed across the east-central and western Pacific, although they were only slightly evident in the monthly average. Upper-level wind anomalies were westerly over the eastern Pacific. Overall, the oceanic and atmospheric conditions reflected ENSO-neutral. The majority of models in the IRI/CPC plume continue to predict the onset of El Niño sometime during the Northern Hemisphere fall and continuing through the winter (Fig. 6). The forecasters also favor El Niño formation during the fall, and are leaning toward the more conservative model guidance that indicates a weak El Niño event. The persistence of above-average subsurface temperatures and continuing flare-ups of westerly wind anomalies also support the eventual development of El Niño. In summary, there is a 50-55% chance of El Niño onset during the Northern Hemisphere fall 2018 (September-November), increasing to 65-70% during winter 2018-19

So they have only just reduced their forecast slightly to 50%-55% chance but still S/O/N which is remarkable - they surely should have changed it to at least O/N/D. Your other sources include the IRC/CPC, who partially updated their output but their next full monthly update for all the main models comes out on Sept 19th. It will be interesting to see how much (or little) the model consensus has changed since mid August. it looks like your other sources were just updated to a few days ago, just prior to the recent set back. All my comments directed to at least a one month delay are only a very small part of this. I look forward to debating the underlying reasons, some of which have been mentioned and I've posted on them before. More this weekend. David

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Ah yes, the tropical Pacific, lets go there. It's time to get comprehensive about ENSO.....

First up are we going to actually have an El Niño? The question on everyone's lips. The answer to this is still not clear at all, primarily because the models have converged and made their consensus. For example, the NMME forecast, featuring the main North American ENSO ensembles, go from a full on Niño with CFS, to the CMC models that show a borderline Niño at best, to the NASA model, that is pretty stagnant and stays warm neutral.

In contrast, the JAMSTEC model shows a fully strong Niño event. Which I think has been consistently forecasting for a while.

To add to the above models, the ECMWF shows a fairly weak EP El Niño, and the Met Office (UKMET) forecasts a slightly stronger, perhaps moderate El Niño event. And as @Blessed Weather shows, the brand new ACCESS (developed from the same core as the UKMET's) model shows an El Niño developing.

But with the graphics posted by @Bring Back 1962-63, that show a warm neutral Niño not really moving anywhere, are we going to move towards an El Niño. Many of the above models do take into account this neutral period, and still come out with a fairly strong El Niño event. One of the more interesting trends to examine with these graphics, is that Niño 3 (more Eastern Pacific) is much more neutral than Niño 4 (more Central Pacific). So with this in mind, it would seem that it would be easier to reach Central Pacific Niño or Modoki Niño. One thing all the models (that I have examined) are clear on is that we aren't going to see cold Niño 1+2 SSTs. Most show warm neutral and often Niño level warmness in the region. This shows that we may be in for warming across both the Eastern Pacific and Central Pacific regions in general. This is a sentiment echoed in my last blog update here:

Quote

During a true Niño Modoki, you see cooling around the South American coast at the equator, this doesn't happen here. Yes it is weaker than the warm anoms further out into the Pacific, but they aren't cooling. This is why none of the Modoki index forecasts I have seen show this as a proper Modoki, because of the warm Niño 1+2 anomalies off South America. This is why I think this event carries both hallmarks of ENSO in various ways, as we all know, no two ENSO events are alike.

The warm subsurface temps are around the Dateline in the observations over NH summer. But CFS shows them moving up (as expected), but also eastwards. And we have started to see this a little bit this month. This creates a warm NIÑO 3 (Eastern Pacific) and NIÑO 4 (Central Pacific).

So maybe a bit of both? If we manage to get one for the most part....

We are starting to see some movement in the last month or so, from the atmosphere, in this example from the SOI and Dateline cloudiness.

SOI is moving more negative since June, an indication of a move towards Niño.

And Dateline cloudiness starting to shift towards negative OLR values which are associated with an Niño event. But from both of these indicators, we really need a follow through towards Full Niño.

Another indicator, the AAM or Atmospheric Angular Momentum has also been noticeably Nina-esque, as noted by this Victor Gensini chart. -AAM correlates with a generally Nina like atmosphere. And remember that there is a difference between the Atmospheric Niño indicators and the Oceanic Niño factors, because they are sometimes not correlated to each other.

It has been slightly heading positive over a monthly timescale, but still fairly negative moving towards neutral (much to the denial of CFS and Bias Corrected GEFS at the moment). Trade winds are also neutral, with several WWBs in the Pacific over the last few months, but now we are heading into a period of big easterly trades in the Central Pacific region in particular. You want weak/westerlies for an El Niño.

This all shows us that we are a long way from any form of a Niño, not until November at least. And my tip is for a warm Weak El Niño in both the Eastern Pacific and Central Pacific regions. This could aid a -AO and Eastern troughing, while also giving California it's big snow dosage. But on the other hand, my other tip is for the atmospheric enso factors to stay warm neutral, and the GWO/AAM to stay neutral with entrances to both +AAM (Niño) and -AAM (Nina) territory. This could make for a very interesting up and down winter for all regions IMO.

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Another indicator, the AAM or Atmospheric Angular Momentum has also been noticeably Nina-esque, as noted by this Victor Gensini chart. -AAM correlates with a generally Nina like atmosphere. And remember that there is a difference between the Atmospheric Niño indicators and the Oceanic Niño factors, because they are sometimes not correlated to each other.

My own angle on analysis and benchmark for monitoring is highly symmetrical with this particular aspect of thinking and the importance attached to the differences. as stated.

As I see it, when we are looking at the atmosphere/ocean relationship and trying to incorporate that (plus a variety of other drivers) into a geopotential height anomaly NWP framework pattern, whether that is shorter or longer term - the bread and butter starting consideration is the precise relationship that the atmosphere adopts to the ocean base state. In that sense, looking at the ENSO base state per se is not going to give any accurate foresight into NWP evolution beyond the usual broad-brush teleconnectic assumptions. Its not that these are not helpful - its just that it leads to some x+y assumptions which are nowhere near as linear as they may appear at face value.

These principle key beliefs, plus a whole load more, are why I place so much faith in the Global Synoptic Dynamical Model (GSDM) as a starting point to my own study and curiosity into matching up weather patterns according to the balance, or budget of wind-flows in the global atmospheric circulation at a given time - which in turn can give such good clues and insight as to how weather patterns may evolve both in the shorter and longer terms.

When I speak of wind-flows, largely this refers in simple English to the movements and velocity of the Jetstream. Tropospherically, within the tropics and extra tropical boundaries where momentum energy flux constantly interchanges to alter wind-flow according to angular momentum budgets, the Pacific is a large engine room of upstream and downstream control on circum-global weather patterns and why the relationship of the atmosphere to the complex changes that occur within the ENSO zones are such an important consideration.

So enough background and good vibration appreciation of the concepts, how about some analysis consideration of some background to the here and now vs the possible way ahead:

There is clearly no need for me, as part of my own assessment, to reproduce the data that the good folk so far have provided as part of the jigsaw on this subject. But to further investigate the GSDM atmospheric key responses provides what I believe is a very reliable barometer to the processes involved

I was well aboard the Nino-esque low tropical frequency signal and +ve relative AAM anomaly gravy train during the latter part of the summer following the brief , but still significant, coupling of the atmosphere vs ocean that took place in late July. The periodicity (timeline recurrence) of low frequency tropical signalling had been consistently very buoyant right back to prior to the SSW that took place in February. This pattern had continued right into the summer - culminating in the eastward progression of that standing wave signal during July into the Pacific

This drove both angular momentum tendency and total global atmospheric angular momentum into +ve territory, briefly - but still not replicating the spike attained during the very temporary reversal of the La Nina standing wave that was the culmination of the tropical>extra tropical momentum transport that 100% destabilised the stratospheric vortex in late winter. A retrospective plot of the The Global Wind Oscillation, which is a plot depiction of total global wind-flow in the atmospheric circulation and therefore a reflection of where AAM sits against parity,isn't currently avaialble by way of further illustration - but it laddered up into the El Nino attractor phases 5,6 and 7 in reflection of the strength of the momentum transport anomaly

The long domination of the La Nina standing wave that had prevailed up to the SSW in February - as depicted by how much time has been spent with greater -ve or easterly trade wind domination at the expense of westerly wind additions added to the atmospheric circulation,

and number 2:

Just how much the atmosphere has still struggled to shake off the shackles of this Nina legacy since the SSW, despite the progression of the ENSO ocean base state to take on a more Nino-like spatial status, at least within the central Pacific

Its this context, which I think illustrates that' its the atmospheric response in terms of how the tropics and extra tropics process easterly (or -ve momentum flux) and westerly (or +ve momentum flux), that determines the arrangements of the longwave hemispheric patterns - as also dictated (augmented or detracted) through natural seasonal wavelength changes.

This being much more relevant and important in this respect in my opinion than the ENSO base state per se despite its changes away from a La Nina state in this time. ENSO base state relationships with the atmosphere can manifest themselves in a variety of ways from one matched up face value scenario to the next. Especially if we take other pernicious drivers like unstable sea ice patterns and associated superimposed warming forcing into account which further amplify and distort the synoptic patterns that occur as manifestations of those variable relationships. The days of the analogue and "one size fits all pattern match" is on stony ground. At least for those who attempt seasonal forecasts out there.

This summer in 2018, despite the barometer reflection of the atmosphere lagging the ocean Nino progression with a stubborn Nina-like circulation the gradual warming profiles of the Pacific through repeated oceanic convectively coupled kelvin wave activity ....

...…...serving to move bodies of sub surface water eastwards and to the surface to increase the spatial extent of warming within the ENSO profile.

I think this tweet from MV in late August summed up that situation

Importantly though, the movement of the low frequency tropical signal though late July had already started coupling up and imprinted the atmosphere onto the newly developing El Nino standing wave.

This might have appeared to represent a real coupled shift regime at last. Tentative and provisional as this move was, it was the first signal since the huge momentum processes leading up to the SSW that tha atmosphere finally wanted to go along with the shifting base state. Its been this (and admitted desire to see change out of a rut!) that had driven my own enthusiasm for a slow, but steady process towards a weak El Nino state during September and October and establishing more generally into the late part of this season and early winter.

This summer seasonal momentum has not carried though however, much as previous analysis on this page has noted and by the AAM anomaly chart which, as illustrated above, has slipped back to previous generally -ve status.

If we take a look at frictional torque tendency...…

……..then resumption of the Nina type signal of repeated easterly trade wind propagation has occurred since mid August around 20 to 30N which has created a -ve tendency to wind-flows and negated/supressed the Asian jet extensions in the extra tropics that are triggered by both low frequency tropical convection attempting to head into the Pacific, and the micro scale cyclonic activity as represented by the fledgling Nino standing wave trying to get implemented

The persisting -ve South Pacific Oscillation largely responsible for this - meaning anomalous heights in the South Pacific with trade winds emanating north from the region and counter-acting the ENSO warming induced by westerly wind bursts c/o of CCKW, MJO and ACE related tropical activity.

These countervailing trade bursts showing up on the Hovmollers wind anomaly plots as shaded blue close to the dateline

Where the extra tropical westerly wind bursts are met by these tropical trade wind easterlies, then an eddy and amplification in the jet stream occurs. This is effectively the inflexion point of the -ve frictional torque response around 30N - with height anomalies propagating polewards from the tropics into the North Pacific and displacing atmospheric disturbances downstream over the US.

.......and the effect of falling frictional and mountain torque tendency impacts on relative and global atmospheric angular momentum and is reflected by the GWO back towards a low amplitude La Nina type Phase 1 signal

Further downstream from the Pacific, the response of the deceleration of the jet in the Pacific is to also

bolster sub tropical high pressure in the Atlantic c/o of both Bermuda and Azores ridges. The easterly trade winds emanating from the tropics help steer the developing tropical activity coming off the AEW with minimal wind shear to aid their development. Much as Florence and her family are more than amply demonstrating at present as everyone is aware.

The tropics are very much engine of pattern change, and the periodicity of the MJO cycle points to the look out for a next amplitude cycle. AAM modelling, as mentioned, has been and still is persistently bullish about an upturn in AAM tendency relative to increased low frequency signal.

Its this, that is required to redress the AAM budget within both the tropics and extra tropics to induce a more sustained and greater +ve frictional torque and extra tropical +ve momentum response as westerly winds change the budget of wind-flows (essentially re-configure the jet stream patterns from upstream).

Converse to the processes within a -ve frictional lowering angular momentum signal, increased +ve westerly wind momentum gaining the upper hand results in an increased Asian jet extension, which serves to de-amplify the sub tropical high pressure in both the Pacific and then downstream in the Atlantic - and in the process change the greater balance of convectively coupled ocean>atmosphere cyclonic/hurricane activity back to the Equatorial Pacific

The EPS VP200 convection anomaly depict a changing signal in the 15 day period, with some credence to greater westerly wind activity and in turn a cessation of the "destructive" Nina-like action on the ENSO zone - and with warming from the sub-surfaces replacing cooling.

The AAM budgets and the GWO will ultimately provide for me the litmus test of how the atmosphere responds in reality away from model forecast suggestions

The GWO response would be one of tracking away from the La Nina type Phase 1,2 and 3 orbit signature and a representation of +ve frictional torque increasing +EAMT into tendency above parity. Such an increase within the AAM wind-flow budget implies the GWO heading back to "transitional" precursor El Nino phase 4.

However, this is only half the story for the extended period for those looking towards late season and on into winter. If the Nino standing wave is to recover assertion, let alone sustain, then the frequency of westerly wind bursts needs to sustain and the low frequency MJO signal provide the sort of eastward amplitude progression of late July to make this happen.

Should this be insufficient, and there is no way of answering this at this time, then question marks will be raised at the particular

ocean vs atmosphere status that will be in place at the same time as the stratospheric vortex is under-going its usual seasonal traditional rituals. This of course relating also to QBO +ve westerly phase descent as well as solar cycling all attendant with Brewer Dobson circulation of ozone transport from the tropical stratosphere in Southern Hemisphere Spring-Summer to the Northern Hemisphere opposite seasons.

There are some great posts already in this fascinating ENSO debate that we've just started on this Teleconnection thread. I strongly recommend the contributions from Malcolm @Blessed Weather, Tom @Isotherm, Tams @Tamara and, of course, Zac @Snowy Hibbo (who should take a lot of credit for creating this specialist thread a few months ago). While a number of us (hopefully a larger number very soon) intend to fully contribute to this fascinating topic as I do, there are some basics that I feel need to be addressed to assist some of the readers (and posters too!). In this post, I had wanted to look at some of the uncertainties over the ENSO state going forward but decided to leave that until my next post in a few days time. I started looking into the difficulties on defining exactly what an El Nino is in terms of when we have one. There is no international consensus over this. It can also be far from straightforward in understanding a single country's definition! Some countries use a different set of measures too. So when various commentators produce their reports, papers, presentations, blogs, tweets and forum posts they may not always be referring to the same definition. There is "some" common ground but not nearly enough.

"Currently, each country has a different threshold for what constitutes an El Niño event, which is tailored to their specific interests. For example, the Australian Bureau of Meteorology looks at the trade winds, SOI, weather models and sea surface temperatures in the Nino 3 and 3.4 regions, before declaring an El Niño. The United States Climate Prediction Center (CPC) and the International Research Institute for Climate and Society (IRI) looks at the sea surface temperatures in the Niño 3.4 region, the tropical Pacific atmosphere and forecasts that NOAA's Oceanic Niño Index will equal or exceed +0.5 °C for several seasons in a row. However, the Japan Meteorological Agency declares that an El Niño event has started when the average 5 month sea surface temperature deviation for the NINO.3 region, is over 0.5 °C (0.90 °F) warmer for 6 consecutive months or longer. The Peruvian government declares that a coastal El Niño is under way if the sea surface temperatures in the Niño 1 and 2 regions equal or exceed +0.4 °C for at least 3 months."

Providing that we take account of these differences, we can start to compare like with like but this does add an extra tier of complexity that can only serve to confuse any reader, including some of the specialists! I vote for a new international standard which may be something of a compromise but at least would pave the way forward for everyone to at least have the same starting criteria (....but read on!). I thought where better to go than to the World Meteorological Organisation (WMO) website. There I found nearly 60 different country definitions and that is just those that are members of the WMO! They did produce this guide in 2006: "Catalogue of Indices and Definitions of El Niño and La Niña in Operational Use by WMO Members" Here's the link: http://www.wmo.int/pages/prog/wcp/wcasp/documents/ENSO-Indices-Catalogue_12062006.pdf

Although some individual countries may have modified their own definitions since 2006, many have not. I'll just show a small sample here and as this is essentially a US weather forum, I had better start with this one:

USA:

Definition of El Niño in use operationally A phenomenon in the equatorial Pacific Ocean characterized by a positive sea surface temperature departure from normal (for the 1971-2000 base period) in the Niño3.4 region greater than or equal in magnitude to 0.5°C, averaged over three consecutive months. . Definition of La Niña in use operationally A phenomenon in the equatorial Pacific Ocean characterized by a negative sea surface temperature departure from normal (for the 1971-2000 base period) in the Niño3.4 region greater than or equal in magnitude to 0.5°C, averaged over three consecutive months

This is the definition used by NOAA (except that it goes further than this (more later below). Many other countries do now use this or a very similar definition. Some countries do not use any definition at all.

UK:

Definition of El Niño in use operationally The Met Office does not currently use an objective definition of El Niño or La Niña. Because links between El Niño/La Niña and European climate are weak it would be very difficult to define an index threshold that would be suitable or meaningful for the UK region. At present the Met Office prefers to provide information in the form of indices that can be interpreted for local application by forecast users.

When I read this, I was very surprised! As that was over 12 years ago, I checked on the UK Meteorological Office website. While they still do provide their own definition, they have adopted the US NOAA definition or at least refer to it.

Australia:

Definition of El Niño in use operationally At present the Bureau of Meteorology does not employ formal definitions to trigger declarations of events at either end of the El Niño – La Niña cycle, but rather uses various indices as assessment tools. The assessment of El Niño/La Niña status is conducted within a scientific yet largely subjective framework and encompasses at least one formal meeting (The Monthly Climate Meeting) per month of operational and scientific staff to discuss the full range of analysis of the atmospheric and ocean state. This includes examination of the indices listed above, as well as proxy indicators such as trade winds, high cloud amount/outgoing longwave radiation, ocean subsurface temperatures, sea surface temperature distribution and model outputs. This assessment is used to develop the text for the Bureau's “ENSO wrap up” discussion, updated weekly in times of El Niño development, and publicly available on the web (http://www.bom.gov.au/climate/enso).

Now, I was already aware that Australia is one of a number of countries that use a very different approach and Zac would have been brought up on this one and will often refer to it. They also use a wider series of measures:

Index (indices) in use operationally  Troup Southern Oscillation Index (SOI) - The standardized anomaly of the Mean Sea Level Pressure difference between Tahiti and Darwin.  Niño1, 2, 3, 3.4, and 4 Sea Surface Temperature (SST) indices.  Multivariate ENSO index (MEI) - A weighted average of the main ENSO features contained in six variables: sea-level pressure, the east-west and north-south components of the surface wind, SST, surface air temperature, and total amount of cloudiness.

Since Australia developed this way of measuring ENSO, many other countries (mostly in the southern hemisphere) have adopted it or a form of it.

India:

Definition of El Niño in use operationally An oceanographic phenomenon in the equatorial Pacific Ocean, characterized by a positive sea surface temperature departure from normal in the Niño3.4 region greater than or equal in magnitude to 0.5°C. The base period for the normal is 1971-2000. To classify as a full-fledged El Niño episode, this threshold must exceed for a period of at least 5 consecutive months.

Like some others, India partly adopts the US definition of the Nino 3.4 region and the +0.5c threshold but note that they extend the 3 month period to 5 consecutive months (more in a minute).

I put this one in to make a point. Some Asian countries focus, quite understandably, on the strong ENSO impacts on their monsoon season. There is a strong correlation with the +ve phase of the SOI (Southern Oscillation Index). On the other hand, India do not use this method!

Peru::

Index (indices) in use operationally  Sea surface temperature anomalies in the equatorial Pacific (Niño4, Niño3.4, Niño3, and Niño1+2) and at coastal stations;  Mean and anomalous subsurface temperatures in the equatorial Pacific and along the Peruvian coast;  Variations in the depth of the 15°C isotherm;  Longitudinal position of the 27°C and 28°C isotherms in sea surface temperatures;  Mean and anomalous low-level (below 850 hPa) zonal winds in the equatorial Pacific;  Pressure systems at 200 hPa near the Peruvian coast and tropical convection;  Others: OLR (outgoing longwave radiation); SOI (Tahiti-Darwin Southern Oscillation Index); MEI (Multivariate ENSO - El Niño-Southern Oscillation - Index); intensity and configuration of the South Pacific anticyclone and minimum air temperature along the coast; biological indicators of warm and cold waters between 50 and 100 nautical miles from the coast. 5. Definition of El Niño in use operationally  Positive sea surface temperature anomalies greater than 1°C in the Niño4, Niño3.4 and Niño3 regions and anomalies greater than 2°C in the Niño1+2 region and coastal areas;

Arguably, Peru is the closest country and in the most direct firing line of an El Nino episode. They go way beyond the basic definition and consider many more variables and measures. They seem to incorporate almost all the other countries' criteria and even more besides! I'm aware of some papers produced by Peruvian (or other South American) meteorologists and I shall seek them out to see why they adopt this approach. It may well be worth considering why they go into this level of detail and what predictability benefits they derive from them. You can see that they are taking account of surface, sub surface and deeper ocean temperatures and air pressure patterns. The "South Pacific anticylone intensity" is fascinating. The term SPO (south Pacific oscillation) only came into use during the last few years (2013 I believe) but this would seem to be a general reference to it and this was the basis they used in 2006 and it's likely that they used it much earlier than that. We may well find that there is some very useful medium term research available - I'll conduct an investigation. if I find any useful papers, I'll place them in the Research Portal and we can review them on here as part of our debate. The wider ramifications may be that it will help with assessing erratic developments and stalls in the progress towards an El Nino, like we've seen recently - the cold current upwellings in the east and their spread along the equator (driven by a -ve SPO) battling with the warmer surface currents. If we could throw in AAM (atmospheric angular momentum) , the torques, the GWO (Global Wind Oscillation) phases and Kelvin wave activity into the equation, we might have some more answers? Apart from stalling information, this Peruvian data might assist in determining the flavour of an El Nino - an east or central Pacific based one (Modoki) or a sub mix.

Right, I've shown enough examples to demonstrate the diversity. Whilst I appreciate that many countries see very different impacts from an El Nino event I would still say that they could easily adopt the NOAA definition and then superimpose their own parameters to adapt to their own Nino or NIna impact assessments and predictions. From now on, I will focus on the NOAA definition. This appears to have evolved since 2006. I tried to find a confirmation of that earlier definition and when (or if) any changes took place. To show what I mean, I repeat their 206 definition as printed by the WMO:

2006 El Nino definition: A phenomenon in the equatorial Pacific Ocean characterized by a positive sea surface temperature departure from normal (for the 1971-2000 base period) in the Niño3.4 region greater than or equal in magnitude to 0.5°C, averaged over three consecutive months.

Now the current NOAA Climate Prediction Center (part of the National Weather Service) definition: The onset of an El Nino episode when the 3-month average sea-surface temperature departure exceeds 0.5c in the east-central equatorial Pacific between 5N-5S and 170W-120W (the Nino 3.4 region) - note: this is as previously but then they add this: For historical purposes, periods of below and above normal SSTs are colored in blue and red when the threshold is met for a minimum of 5 consecutive overlapping seasons. Their full definition is shown in their ENSO table below:

Now, Malcolm @Blessed Weather kindly brought something to my attention this morning and I seem to have made an error in my last post (and a couple of previous ones) when I criticised NOAA for retaining their September (was 60%) 50% chance of an El Nino developing this fall (defined as S/O/N) and said that this was almost mathematically impossible. I wrongly considered that we take an average for each month and then roll them up until we get 3 consecutive months with with an average of +0.5c or more. As Malcolm correctly says, if one reads the wording carefully, it is the average over any consecutive 3 month period. So September could be well below the 0.5c threshold (as indeed it is) but October and November could end up well above and sufficiently so to pull the 3 month average over the threshold. So, I apologise for misleading anyone (if you noticed my error!).

Furthermore, the addition to their official definition is that the threshold must be exceeded for a minimum of 5 consecutive rolling/overlapping 3 months periods. That is why in the table above reds (El Nino) and blues (La Nina) do not run for less than 5 periods. For example the long La Nina episode that ran from M/J/J 2010 until F/M/A 2012 was broken by the M/J/J 2011 when the average fell just below the threshold. Malcolm has prepared an excellent chart to demonstrate this much more easily and I told him that he must take the credit for it and post it himself

What Malcolm's comments did was cause me to research all this today and pull this post together. Some of the detail may not be that relevant but it has thrown up some fascinating variations. Overall, as I commented in several earlier posts, the NOAA definition (or any other for that matter) is actually a very crude measure. We have seen Nino-like and Nina-like conditions while the Nino 3.4 region has been weakly +ve ( mostly in the +0.05c to +0.5c SST anomalies range) since June. The Atlantic hurricane season has shown an amazingly rapid response to "seemingly" relatively minor ENSO changes and has been an excellent barometer of ENSO impacts. It started early (May into early June) with several hurricanes when the recovery from La Nina conditions was just underway. Then that rise peaking at 0.5c for only one day but remaining above +0.2c from late June to mid July killed all the activity. Then that fall back to +0.1c was sufficent to bring about some Nina-like conditions again and the Atlantic burst into activity. Despite all the named storms showing in the Atlantic, only Isaac is still actually in the "tropics" and tropical activity has slowed down for the last few days and this is just after that rise from early September to just 3 days ago. Now we have seen the sharpest set back since mid June and this may well be enough to regenerate the tropical Atlantic activity.

As I've been demonstrating there is far more to it than just the Nino 3.4 region. I posted the charts for all 4 regions yesterday on here.

Meanwhile the east Pacific has just warmed to it highest level of the year or since before the last La Nina begun. This is effectively a reversal of the warmer CP and cooler EP and, even if we see a recovery towards an El Nino later in the year, may mean that it is not a CP based one (or so-called Modoki) as others have alluded to.

I'll do a comprehensive assessment of NOAA's weekly report on Tuesday and look into sub surface currents and other influences to (hopefully) complement what the others are posting.

Everyone is very welcome to contribute to this debate and ask questions. David

There are some great posts already in this fascinating ENSO debate that we've just started on this Teleconnection thread. I strongly recommend the contributions from Malcolm @Blessed Weather, Tom @Isotherm, Tams @Tamara and, of course, Zac @Snowy Hibbo (who should take a lot of credit for creating this specialist thread a few months ago). While a number of us (hopefully a larger number very soon) intend to fully contribute to this fascinating topic as I do, there are some basics that I feel need to be addressed to assist some of the readers (and posters too!). In this post, I had wanted to look at some of the uncertainties over the ENSO state going forward but decided to leave that until my next post in a few days time. I started looking into the difficulties on defining exactly what an El Nino is in terms of when we have one. There is no international consensus over this. It can also be far from straightforward in understanding a single country's definition! Some countries use a different set of measures too. So when various commentators produce their reports, papers, presentations, blogs, tweets and forum posts they may not always be referring to the same definition. There is "some" common ground but not nearly enough.

SNIPPED

Now, Malcolm @Blessed Weather kindly brought something to my attention this morning and I seem to have made an error in my last post (and a couple of previous ones) when I criticised NOAA for retaining their September (was 60%) 50% chance of an El Nino developing this fall (defined as S/O/N) and said that this was almost mathematically impossible. I wrongly considered that we take an average for each month and then roll them up until we get 3 consecutive months with with an average of +0.5c or more. As Malcolm correctly says, if one reads the wording carefully, it is the average over any consecutive 3 month period. So September could be well below the 0.5c threshold (as indeed it is) but October and November could end up well above and sufficiently so to pull the 3 month average over the threshold. So, I apologise for misleading anyone (if you noticed my error!).

Furthermore, the addition to their official definition is that the threshold must be exceeded for a minimum of 5 consecutive rolling/overlapping 3 months periods. That is why in the table above reds (El Nino) and blues (La Nina) do not run for less than 5 periods. For example the long La Nina episode that ran from M/J/J 2010 until F/M/A 2012 was broken by the M/J/J 2011 when the average fell just below the threshold. Malcolm has prepared an excellent chart to demonstrate this much more easily and I told him that he must take the credit for it and post it himself

That's a great summary of the various ENSO definitions in use David. As you say, this being a US forum we should mainly focus on the NOAA definition and prognosis in this thread, although with great analysis also undertaken by the Australian and Japanese meteorological bodies, it's always worth looking at their views on ENSO developments.

Thank you for your kind comment about my NOAA 'ENSO calculation' illustration. I've included it below.

And while I'm here, may I say what superb analysis @Tamara and @Snowy Hibbo have posted above. This is a great ENSO discussion going on!

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ENSO DEBATE - A PAPER REVIEW: THE NORTH AND SOUTH PACIFIC MERIDIONAL MODES

During the early stages of our ENSO debate, I thought that it might be helpful to briefly review a few papers and presentations that we have in the Research Portal which I think may be relevant to the current ENSO phase and the "potentially" emerging El Nino episode. I'll start off with this one:

An interannual variability mode in the southeast Pacific with a physical interpretation similar to that of the Pacific meridional mode (PMM) in the North Pacific was recently identified. Both modes have been shown to influence the subsequent development of El Niño–Southern Oscillation (ENSO) events. This study investigates the relationship between ENSO and the two PMMs using observational and reanalysis data. The results show that the South Pacific meridional mode (SPMM) mainly favors the development of sea surface temperature anomalies (SSTAs) in the eastern equatorial Pacific, whereas the North Pacific meridional mode (NPMM) mainly favors the development of SSTAs in the central equatorial Pacific. Both of the meridional modes are considered to be analogous in terms of their physical interpretation and can be important predictors of ENSO when considering different flavors of ENSO. Neither the NPMM nor the SPMM can be precluded as accurate indicators when forecasting particular flavors of ENSO.

This 2016 paper assesses the influences of these two modes on the ENSO state and on the types or flavour of upcoming El Nino episodes. It also considers the north and south Pacific oscillations (NPO and SPO) and the pattern of SST developments (note that they do not use the specific term SPO which had only just been coined shortly before this paper was published). It covers several examples from recent ENSO past events where the influence from one or the other mode dominated as well as how they interact. It starts off with a great summary of the earlier research in this area and how it evolved. I copy some short extracts from the paper below:

Over the past two decades, numerous studies have established a robust relationship between the development of ENSO and the extratropical variability of the atmosphere

Recent studies have shown that most El Niño events in recent decades have been preceded by apparent NPMM (positive phase) activity.

the Pacific meridional mode in the Southern Hemisphere, defined as the South Pacific meridional mode (SPMM), has a larger equatorial signature than the NPMM for the same amount of extratropical variability, particularly in the eastern equatorial Pacific.

the predictability of ENSO events, particularly the specific flavors of ENSO, are closely related to atmospheric and/or oceanic precursors responsible for the excitation of events at certain lead times

The SST-driven meridional circulation in the subtropical southeastern Pacific was relatively significant from the boreal spring to the autumn.

the subtropical precursor in the Southern Hemisphere, which presents different behaviors and influences than the NPMM in our interpretation, was as important as the subtropical precursor in the Northern Hemisphere when considering its contribution to a different flavor of ENSO.

the variability of ENSO related to the NPMM is more confined to the central Pacific and has relatively less influence on the eastern equatorial Pacific, whereas the variability of ENSO related to the SPMM has less of an impact on the central equatorial Pacific.

From the closing discussion:

This study has several potential implications. First, the different influences of the NPMM and SPMM on ENSO, which are associated with the North and South Pacific extratropical variability, were compared in both hemispheres. The differences may account for different ENSO flavors, which are particularly important for the prediction of ENSO. Second, the NPMM and SPMM may also inhibit the development of ENSO events under special backgrounds, which is similar to the 2012 and 2014 ENSO events

when considering the origins of the SPMM, other questions remain. Although the SPMM originates from the South Pacific extratropics independent of ENSO in the previous boreal winter (Fig. 4b), the question of whether the SPMM originates solely or partly from the remote tropical forcing in other seasons according to fully coupled models and observation data requires further study

This study emphasizes the importance of climatic variability of both the Northern and Southern Hemispheres in the tropical Pacific climate, and it suggests that both the NPMM and SPMM in the subtropical Pacific can be important ENSO predictors in the future. Therefore, forecasts of a particular ENSO flavor may be improved, although such forecasts will certainly require further research.

I realise that it can be misleading to quote parts of a paper which may be taken out of context and I strongly recommend that you read the full paper which is quite short and an easy read with some excellent charts and diagrams..

Well this whetted my appetite, so I'll close with a several charts:

PMM in strongly +ve mode but falling this year. As we know, the SST anomalies have changed to some extent since August - so here's the current chart for comparison.

Much of the sub tropical south Pacific tropical has cooled again as has the tropical and eastern tropical Atlantic and the Indian ocean. We need to keep an eye on those rising tropical EPAC ssts and I'll check today's ENSO region ssts. If there's a noticeable change, I'll post these shortly.

NOAA do not yet produce any charts showing the SPO and I've been trying to find some meaningful charts. Perhaps Zac @Snowy Hibbo our resident southern hemisphere specialist can help? I found this:

I imagine that this would be more useful if we read it in conjunction with the MLSP charts.

EDIT: This is an auto updating chart (run by run), so that we can keep monitoring the changes in the the circulation pattern in the south Pacific

The "Stormsurf" chart runs from T+0 to T+180 (just the current updating T+0 shown above). Since Malcolm @Blessed Weather posted that "For ENSO Look South" paper in the portal and reviewed it on here a few weeks ago (near the top of this page) I've been researching the SPO and realise just how important it is - particularly this year in -ve phase and its influence on the El Nino development probably being a significant contributor to the erratic progress As the paper that I reviewed above says, more research is needed. I have some more papers on all this "southern" influence and if this sparks some interest, I'll happily review several more of them on here. The lack of s hem info compared to the n hem is stark and yet we are starting to appreciate the great significance of these SPAC wind and circulation patterns on driving the surface and sub surface currents from further south and the rate and amount of mixing into the equatorial waters.

When I posted yesterday on the different country ENSO definitions, I found those detailed measurement criteria that Peru applies. I've only just started looking at their Met and climate offerings but it looks like I will find some very useful research which is highly relevant to our discussions. Meanwhile, Zac, it really would be useful if you could post some links on the southern ocean models, charts and marine climate. Apart from posting on here, I also want to do further posts on the Arctic thread which includes "Antartica" and it has a strong influence on the southern oceans and (I think) may, at certain times, have a quite direct influence on the SPO. So all this will have a knock on effect on the ENSO state - when, to what extent and how dominant a factor this might be needs to be investigated. If there are papers out there, I'll try to track them down. David